There is known a cryptographic communication network (key sharing network) configured with a plurality of networked nodes that are mutually connected by a plurality of links. Each node has a function of generating and sharing a random number with opposite nodes that are connected by links, and has a function of performing cryptographic communication over the links by using the random number as a cryptographic key (hereinafter referred to as a link key). Moreover, some of the nodes have a function of generating a cryptographic key (hereinafter referred to as an application key), which is a random number, independently of the links, and has a function of transmitting the generated application key to another node via a link. An application in the key sharing network has a function of acquiring an application key from a node, using the application key as a cryptographic key, and performing cryptographic communication with another application. The cryptographic data communication at this time may be performed via a network (application network), such as the Internet, that differs from the key sharing network. An applications and a node may be implemented in an integrated manner. An application and a node may be configured as terminals independent of each other, and an application key may be transmitted and received between the application and the node.
In a node, a function of generating and sharing a random number (link key) with opposite nodes that are connected by links is implemented by using, for example, a technique commonly called quantum cryptographic communication or quantum key distribution (QKD). There is also known, in a node, a technique to generate a random number (application key) independently of links and to transmit the generated random number to another node via a link.
However, the conventional techniques have a problem that a processing delay for generating and sharing the cryptographic key may occur. For example, a configuration in which a link key is used to share the application key may lead to a large processing delay and processing load as compared with a configuration in which simply the link key is used.